Commit of AES Illustrated code to go along with A Stick Figure Guide …

…to the Advanced Encryption Standard (AES) blog post at www.moserware.com

Aes.cs

@@ -0,0 +1,123 @@
+using System;
+using System.Security.Cryptography;
+
+namespace Moserware.AesIllustrated
+{
+    /// <summary>
+    /// Implements the Advanced Encryption Standard (AES) algorithm.
+    /// </summary>
+    /// <remarks>
+    /// See http://www.csrc.nist.gov/publications/fips/fips197/fips-197.pdf for more info, or Google
+    /// "moserware stick figure guide advanced encryption standard".
+    /// </remarks>
+    public class Aes
+    {
+        // AES is just Rijndael with fewer options to tweak.
+        private readonly Rijndael _Rijndael;
+
+        public Aes()
+        {
+            _Rijndael = new Rijndael();
+        }
+
+        public Aes(byte[] key)
+        {
+            _Rijndael = new Rijndael(key);
+        }
+
+        /// <summary>
+        /// The cipher key in (must be 128, 192, or 256 bits)
+        /// </summary>
+        public byte[] Key
+        {
+            get { return _Rijndael.Key; }
+            set
+            {
+                if (!IsValidAesKey(value))
+                {
+                    throw new ArgumentException("Invalid key size (must be 128, 192, or 256 bits)", "key");
+                }
+                _Rijndael.Key = value;
+            }
+        }
+
+        /// <summary>
+        /// Encrypts a block of data.
+        /// </summary>
+        /// <param name="input">The plaintext block.</param>
+        /// <returns>The resulting ciphertext.</returns>
+        public byte[] Encrypt(byte[] input)
+        {
+            return _Rijndael.Encrypt(input);
+        }
+
+        /// <summary>
+        /// Encrypts a block of data.
+        /// </summary>
+        /// <param name="input">The plaintext block.</param>
+        /// <param name="key">The key to use.</param>
+        /// <returns>The resulting ciphertext.</returns>
+        public static byte[] Encrypt(byte[] input, byte[] key)
+        {
+            return (new Aes(key)).Encrypt(input);
+        }
+
+        /// <summary>
+        /// Creates an encryption transform that can be used by the .NET cryptography APIs.
+        /// </summary>
+        /// <param name="cipherMode">The mode if the cipher to use.</param>
+        /// <param name="initializationVector">An initialization vector (if used by the <paramref name="cipherMode"/>, or <see langword="null"/> if not used).</param>
+        /// <param name="feedbackSizeInBits">Size of the feedback register in bits for feedback modes.</param>
+        /// <param name="paddingMode">The style of padding to apply to the last block.</param>
+        /// <returns>An encryption transform that can be used by the .NET cryptography APIs.</returns>
+        public ICryptoTransform CreateEncryptor(CipherMode cipherMode, byte[] initializationVector,
+                                                int feedbackSizeInBits, PaddingMode paddingMode)
+        {
+            return _Rijndael.CreateEncryptor(cipherMode, initializationVector, feedbackSizeInBits, paddingMode);
+        }
+
+        /// <summary>
+        /// Decrypts a block of data.
+        /// </summary>
+        /// <param name="input">The ciphertext block.</param>
+        /// <returns>The resulting plaintext.</returns>
+        public byte[] Decrypt(byte[] input)
+        {
+            return _Rijndael.Decrypt(input);
+        }
+
+        /// <summary>
+        /// Decrypts a block of data.
+        /// </summary>
+        /// <param name="input">The ciphertext block.</param>
+        /// <param name="key">The key to use.</param>
+        /// <returns>The resulting plaintext.</returns>
+        public static byte[] Decrypt(byte[] input, byte[] key)
+        {
+            return (new Aes(key)).Decrypt(input);
+        }
+
+        /// <summary>
+        /// Creates a decryption transform that can be used by the .NET cryptography APIs.
+        /// </summary>
+        /// <param name="cipherMode">The mode if the cipher to use.</param>
+        /// <param name="initializationVector">An initialization vector (if used by the <paramref name="cipherMode"/>, or <see langword="null"/> if not used).</param>
+        /// <param name="feedbackSizeInBits">Size of the feedback register in bits for feedback modes.</param>
+        /// <param name="paddingMode">The style of padding to apply to the last block.</param>
+        /// <returns>An decryption transform that can be used by the .NET cryptography APIs.</returns>
+        public ICryptoTransform CreateDecryptor(CipherMode cipherMode, byte[] initializationVector,
+                                                int feedbackSizeInBits, PaddingMode paddingMode)
+        {
+            return _Rijndael.CreateDecryptor(cipherMode, initializationVector, feedbackSizeInBits, paddingMode);
+        }
+
+        private static bool IsValidAesKey(byte[] key)
+        {
+            // AES only allows 3 key sizes
+            int keySizeInBits = key.Length*Constants.BitsPerByte;
+            return (keySizeInBits == 128)
+                   || (keySizeInBits == 192)
+                   || (keySizeInBits == 256);
+        }
+    }
+}